Slanted roof type rectangular waveguide having walls constructed to suppress unwanted modes



April 1966 TSUNEO NAKAHARA SLANTED ROOF TYPE RECTANGULAR WAVEGUIDEHAVING WALLS CONSTRUCTED TO SUPPRESS UNWANTED MODES Filed on. so, 1963a. L u 4 la. /a.. 56.9. .5 E g. 4

I 2.4 d 2a.- 5.!- 3 a. .54 4 a.

J 4 L0 .3 /a. E195 (d. 35 I 51 6g. 1 5' INVENTOR. 2a.

/ L 3 H15 Arramvev TSUMEOA/AKAHARA United States Patent O 3,247,474SLANTED ROOF TYPE RECTANGULAR WAVE- GUIDE HAVING WALLS CONSTRUCTED TSUPPRESS UNWANTED MODES Tsuneo Nakahara, Nishinomiya-shi, Japan,assignor to Sumitnmo Electric Industries, Ltd., Osaka, Japan, a companyof Japan Filed Oct. 30, 1963, Ser. No. 320,064

7 Claims. '(Cl. 333-73) This invention relates to an improvement on therectangular waveguide. Its objective is to furnish a rectangularwaveguide which will transmit at a low rate of loss only the principalwave that has electric field poralization in the direction of the sidewalls of the tube. To describe it in further detail the object of this.invention is to transmit at a low rate of loss only the principal wavethat has electric field polarization in the direction of the side wallsof the tube, solving the degeneration of the wave flowing in the tube ofthe mode that originally has an equal propagation constant and is in therelation of degeneration.

Other objects and advantages appear hereinafter in the followingdescription and claims.

The accompanying drawings show for the purpose of exemplificationwithout limiting the invention or claims thereto, certain practicalembodiments illustrating the principles of this invention wherein:

FIG. 1 is a graphic representation of the dimensional axes of awaveguide.

FIG. 2 is a view of a hollow waveguide of square cross section with allfour sides continuous.

FIG. 3 is a view of a hollow waveguide of square cross section with aslit longitudinally in the top of an electr c-conductive side.

FIG. 4 is a view of a hollow waveguide of rectangular cross section thefour continuous sides of which have thin layers of loss material anddielectric material on the walls thereof. 7

FIG. 5 is a view of a hollow waveguide of rectangular cross section,three of the walls are continuous andhave their layers of loss materialand dielectric material and a slit longitudinally in oneelectro-conductive side.

FIG. 6 is a view of a hollow waveguide of rectangular cross section, allwalls of which are continuous and the upper wall extends outwardlytowards a ridge.

FIG. 7 is a view of a hollow waveguide of rectangular cross section,three walls of which are continuous and the upper wall extends outwardlytoward a ridge with a slot longitudinally of the ridge.

With a rectangular waveguide which is constituted of anelectro-conductive material uniform in all of the directions (X) (Y)(Z), let (a) and (b) represent the transverse dimensions of thewaveguide which transmit only the wave of TE mode which is usually theprincipal and wave and (A) the wave length of the transmittedelectromagnetic wave respectively. Then it is necessary that (a) and (b)satisfy the following formulae respectively,

(see FIG. 1). i

Now that hands of exceedingly high frequencies have come to be utilizedin recent times, the wave lengths in use are 'becoming shorter andshorter, so that the aforementioned dimensions (a) and (b) of therectangular waveguide becomes smaller and smaller. This results in anincreased transmission loss and lowered power capacity. Consequently,if. a waveguide of a low loss and large capacity is to be obtained alsofor a band of high frequencies, it is necessary to make both or one ofthe said dimensions (a) and (b) greater than the aforementioned limits.In the case of such a waveguide, however, the transmission mode is notsingle, there existing one or more transmission modes of a high order inaddition to the TE mode of the principal wave. Even if only the 'I'Emode is excited as is ideal, the transmission energy is converted intohigh order modes because of the lack of uniformity of the line and itsbends, this causing loss, distortion, etc. 'It is therefore necessary torepress the generation high order modes as far as possible. i

As a means to repress the generation of such high order modes, it wasproposed'to make a rectangular waveguide whose top and bottom walls areof an electro-conductive material and whose side walls are of poorelectro-conductivity in the Z direction and of good electro-conductivityin the X direction, taking advantage of the fact that in the case of TEmode only currents in the X direction flow in the inner surface of theside walls and only currents in the Z direction flow in the center ofthe inner surface of the top and bottom walls. As a result, it has beenshownthat the dimension (a) may be increased to three times theaforementioned limit and the dimension (b) to infinity.

Of TE and TM (m=1, 2, 3 (1:0, 1, 2 however, it is only TE, mode that hasthe current flowing on the surface of side walls in the-X directiononly, and it has been discovered that all the hybrid wave modes (HEmodes) having TE, and TM (mn=l, 2, 3 in the relationship of degenerationin the rectangular waveguide mixed belong to this kind of modes.Consequently, the aforementioned waveguide transmits, besides TE mode,I-IE mode at low loss, so that a transmission line desired to trans mitonly TE mode at low loss is not obtained.

The rectangular waveguide of this invention is characterized in that ittransmits at a low rate of loss only the principal wave that haselectric field polarization in the direction of the side walls of thetube, solving the degeneration of the wave flowing in the tube of themode that originally has an equal propagation constant and is in therelation of degeneration.

The first of the embodiment of this invention is characterized in thatthe side walls facing each other are made poorly electro-conductive inthe axial direction of the tube and electro conduotirve in the directionnormal to the axis and athin layer of a dielectric material or magneticmaterial is provided on the inner surface of each of the said sidewalls.

A second characteristic of an embodiment is that the side walls facingeach other are provided with a thin layer of a dielectric loss materialon their inner, surface and a thin layer of a dielectric material ormagnetic material is provided further on it. A third characteristic isthat one or both of the upper and lower walls facing each other has aninner surface different in efiect from aplane and the side walls facingeach other are made poorly electro-condu'ctive in the axial direction ofthe tube and electro-conductive in the direction normal to the axis.

I will explain the above mentioned characteristics in detail, makingreference to the attached drawings. In the figures, the same symbolsrefer to'the same parts.

FIGURE 2 and FIGURE 3 show embodiments in which the side walls of thewaveguide are made poorly electro-conductive in the axial direction ofthe tube and electro-conductive in the direction normal to the axis anda thin layer of a dielectric material or magnetic material is providedon the inner surface of each of the said side walls.

In FIGURE 2, 1a, 1b are the upper and lower walls made of anelectro-conductive material, 2a, 2b are side walls facing each other,made of electro-conductive material 4 and dielectric material 3placedalternately in the axial direction of the tube, so that it is poorlyelectroconductive in the axial direction of the tube and iselectroconductive in the direction normal to the axis. a, 5b are thinlayers of a dielectric material or magnetic material provided on theinner surface of the said side walls 2a, 2b.

In FIGURE 3, the embodiment illustrated in FIGURE 2 is provided in theupper wall In with slits (d) uniform in the longitudinal direction ofthe tube.

With these embodiments, the degeneration of 'I'F mode and TM mode issolved mainly by the effect of the dielectric material or magneticmaterial provided on the inner surface of the side walls and HE modebecomes no longer the eigen mode and can no longer be transmitted at lowloss. If TE mode whose electric field component is parallel to the wallsurface on the side walls is considered, the other modes sustain anexceedingly great loss due to the dielectric material placed alternatelywith an electro-conductive material to form the side walls, while theloss sustained by TE mode is exceedingly small as compared with othermodes. In consequence, it is possible to transmit only TE mode at a lowrate of loss by suitably selecting the distance between the side wallsfacing each other.

FIGURE 4 and FIGURE 5 illustrate embodiments in which the side walls ofthe rectangular waveguide are facing each other provided with a layer ofloss material on the inner surface and a thin layer of a dielectricmaterial or magnetic material is provided further upon it. In thefigures, the same symbols as those in FIG- URE 2 represent the sameparts. 3a and 3b, and 6a and 6b are the thin layers of a loss materialprovided on the inner surface of the walls. A thin layer 4a, 4b, 5a and5b of a dielectric material or magnetic material is provided further onthem. In FIGURE 5, the upper wall 1a is provided with a slit (d) uniformin the longitudinal direction of the tube.

In these embodiments, the degeneration of TE mode and TM mode is solvedmainly by the effect of the dielectric material or magnetic material onthe inner surface of the side walls, and HE mode becomes no longer theeigen mode and can no longer be transmitted at low loss. If TE modewhose electric field component is parallel to the wall surface on theside walls is considered, the loss sustained by this 'mode from the lossmaterial is exceedingly small as compared with all the other modes.Consequently, it is possible to transmit only TE mode at a low rate ofloss by suitably selecting the distance between these side walls facingeach other.

FIGURE 6 and FIGURE 7 show embodiments in which one or both of the upperand lower walls are made to have an inner surface different in effectfrom a plane. In the figures, only the upper wall 1a has outwardlyextending slanted planes. As in the embodiment shown in at least FIGURES2, 3, 6 and 7, the side walls are made poorly electro-conductive in theaxial direction of the tube and electro-conductive in the directionnormal to the axis, by placing a dielectric material 3 andelectro-conductive material 4 alternately. FIG- URE 7 shows theembodiment of FIGURE 6 in which the upper wall 1a is provided with aslit (d) uniform in the longitudinal direction of the tube.

In these embodiments, because one or both of the upper and lower wallshave a length dilferent in efiect from that of a plane, the degenerationof TE mode and TM mode is solved and HE mode becomes no longer the eigenmode and can no longer be transmitted at low loss. If TE mode whoseelectric field component is parallel to the wall surface on the sidewalls is considered, the other modes sustain a very great loss due tothe dielectric material, while the loss sustained by TE mode isexceedingly small as compared with other modes. Consequently, it ispossible to transmit only TE mode at a low rate of loss by suitablyselecting the distance between the side walls facing each other.

I claim:

1. A rectangular waveguide comprising a tube having upper and lowerwalls with opposite side walls, at least one of said upper and lowerwalls facing each other has an inner surface which is different ineffect from a plane and the side walls facing each other are made poorlyelectro-conductive in the axial direction of the tube andelectro-conductive in the direction normal to the axis.

2. A rectangular waveguide comprising a tube having upper and lowerwalls with opposite side walls, at least one of said upper and lowerwalls facing each other is different in effect from a plane and have aslit uniform in the axial direction of the tube, and the side wallsfacing each other are made poorly electro-conductive in: the axialdirection of the tube and electro-conductive in the direction normal tothe axis.

3. A waveguide comprising a tube having a top and a bottom with opposedsides, said top and bottom consisting of an electro-conductive materialin slanted planes extending toward an apex that is parallel to thelongitudinal axis of the tube, said opposed sides consisting of stripsections alternately in the axial direction of the tube ofelectr-o-conductive material and of dielectric ma terial to make thewhole of each of the opposite sides poorly electro-conductive in theaxial direction of the tube but alternately electro-conductive in thedirection normal to the axis of the tube, and thin layers of dielectricmaterial aud magnetic material on the inner surfaces of said sides.

4. The waveguide of claim 3 wherein at least one of said top and saidbottom of said tube has a slit along the apex in the longitudinaldirection of the tube.

5. A waveguide comprising a tube having a top and a bottom with opposedsides, said top and bottom consisting of an electro-conductive material,said opposed sides consisting of strip sections alternately in the axialdirection, a plurality of electro-conductive material to make the wholeof each of the opposite sides poorly electro-conductive in the axialdirection of the tube but alternately electro-conductive in thedirection normal to the axis of the tube, thin layers of dielectricmaterial and magnetic material on the inner surfaces of said sides, andslanted planes in at least one of said top and said bottom of said tubeextending toward an apex that is parallel to the longitudinal axis ofsaid tube.

6. The waveguide of claim 5 wherein at least one of said top and saidbottom of said tube has a slit at the apex of said slanted planes. 1

7. The waveguide of claim 5 wherein at least one of said top and saidbottom has a slit in the longitudinal direction of the tube.

FOREIGN PATENTS 1,219,805 12/1959 France.

HERMAN KARL SAALBACH, Primary Examiner.

1. A RECTANGULAR WAVEGUIDE COMPRISING A TUBE HAVING UPPER AND LOWERWALLS WITH OPPOSITE SIDE WALLS, AT LEAST ONE OF SAID UPPER AND LOWERWALLS FACING EACH OTHER HAS AN INNER SURFACE WHICH IS DIFFERENT INEFFECT FROM A PLANE AND THE SIDE WALLS FACING EACH OTHER ARE MADE POORLYELECTRO-CONDUCTIVE IN THE AXIAL DIRECTION OF THE TUBE ANDELECTRO-CONDUCTIVE IN THE DIRECTION NORMAL TO THE AXIS.